1. Field of the Invention
The present invention relates to an ultrasonic transducer for use in ultrasonic diagnostic medicine and, more particularly, to an ultrasonic transducer including a two-dimensional sensor array. The present invention also relates to a method of manufacturing such an ultrasonic transducer.
2. Description of a Related Art
In the ultrasonic diagnostic apparatus, it has conventionally been general to use, as the ultrasonic transducer for ultrasonic-wave transmission and reception, a one-dimensional sensor array having piezoelectric elements (piezoelectric vibrators) such as piezoelectric ceramics represented by PZT (Pb (lead) zirconate titanate) or polymer piezoelectric elements represented by PVDF (polyvinyl difluoride). Furthermore, by mechanically moving such a one-dimensional sensor array, a two-dimensional image is acquired whereby a three-dimensional image is obtained by combining a plurality of two-dimensional images together.
In this approach, however, there is time lag in respect of a moving direction of the one-dimensional sensor array. Because of combining together the sectional images different in time, the resultant image will be an obscured one. Accordingly, this is not suited for an object to be inspected such as a living body as in carrying out ultrasonic-echo observations in ultrasonic diagnostic medicine.
For this reason, there is a recent attempt to use a two-dimensional sensor array having ultrasonic-wave transmitting/receiving elements arranged in two dimensions to electrically scan an object to be inspected with an ultrasonic wave wherein a technique of dynamic focusing or the like is used in a depth direction, thereby improving the quality of an ultrasonic image. Namely, by using a two-dimensional sensor array, a two-dimensional image can be acquired without mechanically moving the sensor array, which makes possible to obtain a high quality three-dimensional image.
On the other hand, in order to place a probe having a two-dimensional sensor array into practical application, there is a need to densely integrate a multiplicity of elements for transmitting and receiving ultrasonic waves. Particularly, in the case of using piezoelectric vibrators of the above-mentioned PZT or PVDF as ultrasonic-wave transmitting/receiving elements, there is a necessity of micro-fabricating the elements and wiring to a multiplicity of elements. However, there is difficulty in miniaturizing and integrating elements to an extent beyond that in the present situation. An approach to resolve them is now under consideration.
For example, JP-A-8-186896 discloses an ultrasonic transducer capable of eliminating the electric, acoustic leak between piezoelectric vibrators to improve the characteristic of an emission ultrasonic wave, and method of manufacturing the same. According to the document, the ultrasonic transducer has a plurality of piezoelectric vibrators in two-dimensional arrangement formed by completely cutting a piezoelectric plate for ultrasonic-wave emission, a plurality of drive electrodes each formed on a surface opposed to an ultrasonic-wave emitting surface of the piezoelectric vibrator, a common electrode formed on the ultrasonic-wave emitting surface of the piezoelectric vibrator, and a printed wiring board electrically connected to each of the drive electrodes to supply an externally applied voltage to the drive electrodes.
However, according to the scheme of directly joining together the piezoelectric vibrators and the solder material joined on a copper wiring arranged in the printed wiring board, the number of wiring pieces per unit area increases with increase in the number of piezoelectric vibrators, which requires to miniaturize the copper wiring in its extended portion arranged in the printed wiring board. Due to this, the adjacent ones of solder are apt to contact by the spread of solder, which causes lower in yield or reliability. Further, this scheme causes deviation in joining the solder material to the piezoelectric-vibrator electrodes, which makes it difficult to provide positive contacts. Furthermore, in this scheme, there is encountered a limitation in the number of wiring pieces. Meanwhile, in the case the printed wiring board uses a flexible wiring board such as a polyimide film, the polyimide film readily shrink due to heat, and therefore, it causes a problem that the adjacent ones of solder is put into contact by the shrinkage of the polyimide film.
In order to realize an ultrasonic transducer capable of obtaining a high-resolution ultrasonic image with reproducibility, there is a need to easily and positively carry out joining a multiplicity of precise vibrators to electrodes as well as providing electrical wiring. For this reason, there is a desire to develop a novel method of joining vibrators to electrodes, a novel method of providing wiring, and so on.